The lubrication structure of an engine is configured so that the sliding parts of the engine are lubricated by oil in the crankcase. Various types of oil level detection apparatuses for detecting the level of oil pooled in the crankcase have been disclosed, such as those in Japanese Laid-Open Utility Model Application No. 58-163826, Japanese Laid-Open Patent Application (Kokai) No. 60-331, and Japanese Patent Publication (Kokoku) No. 55-45733.
The oil level detection apparatuses known in Japanese Laid-open Utility Model Application No. 58-163826, Japanese Laid-open Patent Application (Kokai) No. 60-331, and Japanese Patent Publication (Kokoku) No. 55-45733 are provided with a magnetic float switch. The magnetic float switch comprises a float, a permanent magnet housed in the float, and a reed switch for sensing the magnetic force of the permanent magnet. In accordance with these oil level detection apparatuses, a drop in the level of the oil to a preset lower limit level causes the float to move down in accordance with this drop, and the reed switch therefore senses the magnetic force of the permanent magnet housing in the float, whereby the level drop is detected, an indicator lights is lighted, and an alarm is issued.
However, in the oil level detection apparatuses known in Japanese Laid-Open Utility Model Application No. 58-163826, Japanese Laid-Open Patent Application (Kokai) No. 60-331, and Japanese Patent Publication (Kokoku) No. 55-45733, consideration must be given to prevent the reed switch from being affected by an external magnetic field.
In view of the above, efforts are being made to develop an oil level detection apparatus for an engine in which the float switch does not use a reed switch. Such an oil level detection apparatus is proposed in Japanese Utility Model Registration No. 2532891. A summary of the oil level detection apparatus disclosed in Japanese Utility Model Registration No. 2532891 is described with reference to FIGS. 11A and 11B.
FIG. 11A shows an engine provided with an oil level detection apparatus, and FIG. 11B shows a schematic diagram of the oil level detection apparatus shown in FIG. 11A.
The engine 100 shown in FIG. 11A is a general-purpose engine in which oil 102 is pooled in the bottom of the crankcase 101. The engine 100 is provided with an oil dipper 104 for lifting and supplying oil 102 to sliding parts in accompaniment with the rotation of the crank shaft 103, and a float-type oil level detector 111 for detecting the level of oil 102 in the crankcase 101.
The levels of the oil 102 are each set in that the upper limit level L1 is set at the highest point, the lower limit level L2 is set below the upper limit level L1, and the lowest limit level L3 is set below the lower limit level L2. FIG. 11B shows the oil level detection apparatus 110 when the oil 102 has risen to the upper limit level L1.
The oil level detection apparatus 110 either merely provides notification in accordance with the levels L1 to L3 detected by the float-type oil level detector 111, or provides notification and stops the engine 100, as shown in FIGS. 11A and 11B. More specifically, the float-type oil level detector 111 has a float 113 in a casing 112, and an electroconductive vertical rod 114 that is fixed to the float 113. Following is a description of the effects of the oil level detection apparatus 110.
With the engine 100 operating, a drop in the oil 102 to the lower limit level L2 causes the vertical rod 114 to descend together with the float 113 and to make contact with the bottom surface 101a of the crankcase 101. As a result, the path through the battery 115, the alarm lamp 116, the electroconductive ring 112a of the casing 112, the vertical rod 114, and the bottom surface 101a of the crankcase 101 is made electrically conductive. As a result, the alarm lamp 116 is lighted and notification is provided that the oil level is at the lower limit level L2.
Furthermore, when the oil 102 has dropped to the lowest limit level L3, the movable contact 117 disposed on the lower surface of the float 113 makes contact with the fixed contacts 118 and 118. As a result, the engine 100 stops because the ignition apparatus 119 stops ignition operation.
Following is the case in which the engine 100 is mounted in a work machine. The term “work machine” includes stationary and mobile (portable) equipment.
Electric generators, high-pressure washers, and other stationary work machines do not move, and the work machine itself does not significantly shake. The engine 100 mounted in a stationary work machine also does not significantly shake. For this reason, the level of the oil 102 does not vary considerably. Therefore, when the level of the oil drops to a fixed level or lower, the engine 100 automatically stops.
Cultivators or other mobile work machines shake considerably during movement. The engine 100 mounted in a mobile work machine also shakes considerably. For this reason, the level of the oil 102 shakes considerably in comparison with an engine mounted in a stationary work machine. Also, since the oil 102 is lifted by the oil dipper 104, the fluctuation in the oil level is considerable.
When the float 113 vertically moves in accordance with the fluctuations in the oil level, the movable contact 117 also moves. When the movable contact 117 moves considerably in the vertical direction with the oil 102 in a dropped state, the level is detected as having dropped even though the actual level (current level) has not dropped to the lowest limit level L3. As a result, the engine 100 stops. Because of this situation, the engine 100 cannot automatically stop even if the level of the oil has dropped to a fixed level or lower in the case that the engine 100 is mounted in a mobile work machine.
A type of oil level detection apparatus 100 that can automatically stop the engine 100 must therefore be provided when the engine 100 is mounted in a stationary work machine. Also, a type of oil level detection apparatus 100 in which the engine 100 is not automatically stopped must be provided when the engine 100 is mounted in a mobile work machine. Under such conditions, two types of oil level detection-apparatuses 110 for an engine must be provided in accordance with the type of implement such a work machine, more time is needed to manage the machine, and the manufacturing cost increases. Therefore, there is room for improvement.
In view of the above, there is a need for an art that can be used both when the engine is automatically stopped and when the engine is not automatically stopped once the level of the oil in the crankcase has dropped to a fixed level or lower, by using only one type of oil level detection apparatus.
Furthermore, the level of the oil 102 shakes due to the vibrations of the engine 100 when the engine 100 is operating, as shown in FIGS. 11A and 11B. Also, since the oil 102 is lifted by the oil dipper 104, waves are generated on the surface of the oil. In other words, the fluctuations of the oil level are considerable. The vertical rod 114 and movable contact 117 (hereinafter the two are referred to as “movable contact 117”) also move vertically in accompaniment with the vertical movement of the float 113 in accordance with the fluctuations in the oil level.
The movable contact 117 is a switch member that is directly mounted on the float 113 and does not have hysteretic switch operation characteristics such as those of a magnetic float switch. For this reason, if the actual level decreases to the vicinity of the lowest limit level L3 when the oil level has dropped while considerably moving up and down, the movable contact 117 makes intermittent contact with the fixed contacts 118 and 118. In other words, the movable contact 117 can make intermittent contact with the fixed contacts 118 and 118 in spite of the fact that the actual level has not dropped to the lowest limit level L3. Also, when the actual level has dropped to the lowest limit level L3, the movable contact 117 intermittently repeats very short contact with the fixed contacts 118 and 118.
When the engine 100 is stopped, the oil level does not change. The movable contact 117 remains in continuous contact with the fixed contacts 118 and 118 when the oil has dropped to the lowest limit level L3.
The level detection operation by the movable contact 117 and the pair of fixed contacts 118 and 118 is completely different depending on whether the engine 100 is stopped or operating. Due to this fact, consideration must be given for more accurate and reliable detection regardless of the engine operating state.
In view of the above, there is a need for an art that can allow the oil level of an engine to be more accurately and reliably detected when the engine is stopped or operating.